Current video coders (MPEG, H.264, HEVC, . . . ) use a block-wise representation of the images to be coded. The images are subdivided into blocks of square or rectangular shape, which are liable to be subdivided in their turn in a recursive manner.
For at least one block considered from among the various blocks obtained, a prediction of pixels of the block considered is implemented with respect to prediction pixels which belong either to the same image (Intra prediction), or to one or more previous images of a sequence of images (Inter prediction) which have already been decoded. Such previous images are conventionally called reference images and are preserved in memory either at the coder or at the decoder. In the course of such a prediction, a residual block is calculated by subtracting the pixels of the block considered, from the prediction pixels. The coefficients of the calculated residual block are then quantized after a possible mathematical transformation, for example of discrete cosine transform (DCT) type, and then coded by an entropy coder. The coded data are written into a data signal intended to be transmitted to a decoder.
Said data signal comprises in particular:                the type of prediction (Intra prediction, Inter prediction, default prediction carrying out a prediction for which no information is transmitted to the decoder (“skip”));        the mode of prediction (direction of prediction, reference image component, . . . );        the type of subdivision into sub-blocks;        the type of transform, for example 4×4 DCT, 8×8 DCT, etc. . . . ;        the values of pixels, the values of transformed coefficients, amplitudes, signs of quantized coefficients of the pixels contained in the block or the sub-block considered.        
Once the data signal has been received by the decoder, the decoding is done image by image, and for each image, block by block. For each block, the corresponding elements of the data signal are read. The inverse quantization and the inverse transformation of the coefficients of the blocks are performed to produce a decoded residual block. Next, the prediction of the block is calculated and the block is reconstructed by adding the prediction to the decoded residual block.
More precisely:                an Intra prediction of a block of a current image consists in predicting pixels of this block with respect to pixels of the current image which have already been coded and then decoded and which may be situated in various predetermined directions, for example thirty-five in the HEVC standard,        an Inter prediction of a block of a current image consists in predicting certain coding information associated with this block, such as for example:                    the temporal motion vector of the current block with respect to a temporal motion vector associated with a block of reference pixels,            the pixels of the current block with respect to the pixels of a block of reference pixels which is pointed at by the temporal motion vector and which is situated in an image other than the current image to which the current block belongs.                        
Such types of prediction are very different from one another. Sometimes, it turns out that the type of prediction (e.g.: Inter) selected in such a coding/decoding scheme is poorly suited to the current block to be coded/decoded.
This results in unsatisfactory compression performance.